Large inhalable particles exist in the workplace and can constitute a substantial amount of inhaled exposure (50% or more). Particles >30 mm primarily deposit in the oral and nasal cavities. Symptomatic health effects (acute or chronic rhinitis, chronic pharyngitis, chronic sinusitis, nasal cancer, and chronic laryngitis and gastro- intestinal diseases) occur in many industries, indicating the presence of these large inhalable particles. However, no instrument currently exists that is capable of measuring particle sizes between 30 and 100 mm. Large particles settle out quickly (terminal settling velocity of 100 mm particle = 0.3 m/s), requiring a real-time instrument to capture the timing and magnitude of the exposure. This project has three specific. The first aim is to design a portable inhalable particle spectrometer to measure inhalable aerosols as a function of particle size in real time. The second aim is to evaluate the sampling efficiency and other performance measures for this instrument in both calm air and low-wind speed environments. The third aim is to evaluate the size distribution of aerosols as a function of job task in two workplaces: a dairy parlor and in a machining shop. The outcome of this project will be an instrument capable of measuring inhalable aerosol size distributions. The ability to measure large inhalable particles will allow u to evaluate a hazard that up until now has remained un-quantified. Such measures will allow improved assessment of worker exposure, better selection of appropriate control methods, and thus, improvements to worker health. Successful development of the proposed instrument will enable researchers to make fast, accurate aerosol size distribution measurements with a small, lightweight, and relatively inexpensive device.